This invention relates to a composite fabric, and more particularly to a nonwoven composite fabric which is gas-permeable but impervious to liquids, such as water.
Gas-permeable, water-impervious nonwoven fabrics have been developed for use in various applications. For example, nonwoven fabrics have been used commercially as a housewrap to form a barrier to air infiltration. A commercial example of such a fabric is the product Tyvek.RTM. sold by Dupont.
Gas-permeable, water-impervious nonwoven fabrics are also used in various medical applications as a barrier to the passage of fluids or microorganisms. Such fabrics are used as hospital gowns, surgical drapes, CSR wraps, and the like. Nonwoven fabrics of this type are described, for example, in the following U.S. Pat. Nos.: 4,041,203; 4,196,245; 4,310,594; 4,504,539; 4,508,113; 4,555,811; 4,657,804; 4,766,029; and 4,863,785.
Typically, the nonwoven barrier fabrics of this general type are of a composite or laminated construction and employ one or more microporous layers to provide the barrier properties to the fabric and one or more layers of reinforcing fibers or filaments to lend strength to the fabric. For example, the microporous layer may be a meltblown web of microfibers produced, for example, as described in Buntin et al., U.S. Pat. No. 3,849,241. The layer of reinforcing filaments may be a spunbonded nonwoven fabric.
In the manufacture of this type of fabric, the respective nonwoven layers are typically bonded together thermally to form a unitary composite fabric. For example, the thermal bonding may be carried out by passing the nonwoven layers through a heated patterned calender and partially melting one or more of the fibrous components. Without sufficient melting, the fabric laminate will have poor inter-ply adhesion. However, unless the thermal bonding conditions are accurately controlled, the possibility exists that the thermal bond areas may be heated excessively, which can destroy or compromise the barrier properties of the meltblown barrier layer.
Also, many of the prior fabrics experience a loss in tear and tensile properties when the layers are laminated by thermal calendering. Temperatures required to bond the layers together may cause some relaxation of the fiber orientation of the reinforcing fibers or filaments.
Also, the resulting composite fabric may have very low elongation. As a result, when the fabric is subjected to load, it tends to yield catastrophically by tearing rather than by stretching. Greater stretch would result in a tougher structure with higher tear properties and less prone to punctures and rips.